1. Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium. The present invention also relates to a magnetic recording medium produced the method.
2. Description of the Related Art
Demand is rising for magnetic recording mediums with increased recording density and lower cost. To adequately meet this demand, it is critical that magnetic thin films have both high coercive force and low noise. Accordingly, alternative compositions and structures for a magnetic layer, a non-magnetic under-layer, and various laminating methods have been proposed.
Japanese Patent No. 2806443 provides a magnetic recording medium with high coercive force by controlling oxygen concentration in a metallic under-layer and/or a ferromagnetic layer at 100 wt ppm or less. In this disclosure, a magnetic recording medium has a ferromagnetic metal layer formed directly on a substrate or through an under-layer on a substrate. The ferromagnetic metal layer disclosed is composed of a cobalt-base alloy. The materials for the metallic under-layer include chromium, titanium, tungsten and alloys of these metals.
Recently a magnetic layer, commonly called a granular magnetic layer, has been proposed. This granular magnetic layer commonly has a structure composed of magnetic grains and a surrounding non-magnetic non-metallic substance, such as oxide or nitride.
Japanese Unexamined Patent Application Publication No. H8-255342, discloses a method for attaining low recording noise by forming a granular recording layer in which ferromagnetic grains are dispersed in a non-magnetic film. This publication discloses a manufacturing method comprising the steps of sequentially depositing a non-magnetic film, a ferromagnetic film and a non-magnetic film on a non-magnetic substrate, and heat-treating the laminate.
The magnetic layer in this disclosure includes a main component of cobalt or an alloy containing cobalt. The non-magnetic film is either a metal, an oxide, a nitride, carbon, or carbide.
U.S. Pat. No. 5,679,473 discloses a granular recording film in which each magnetic grain is surrounded and individually separated by a non-magnetic oxide. The recording film is formed by means of RF (radio frequency) sputtering using a CoNiPt target containing an oxide, such as SiO2. This type of recording film achieves a high coercive force Hc and a low noise.
According to this disclosure, low noise is achieved for the following reason. Since each of the magnetic grains in this granular magnetic film is physically separated by a grain boundary of non-magnetic non-metallic phase, magnetic interaction between the magnetic grains is reduced and formation of the magnetic domain wall with a zigzag shape at the transition region of a recording bit is sufficiently suppressed.
Noise in a recording medium is caused by fluctuation of magnetization due to magnetic interaction between magnetic grains (that constitute the medium), and the size of the grains. To maintain high signal-to-noise ratio (SNR), sufficient to sustain enhancement of the recording density, it is necessary to hold the number of magnetic grains per bit cell at greater than a certain value. In other words, it is necessary to minimize the magnetic grain size.
Unfortunately, where large exchange interaction arises between the magnetic grains, the minimization of magnetic grains frequently does not necessarily result in minimization of a unit of reversed magnetization. Therefore, it is additionally desirable to suppress the exchange interaction between the grains and minimize the unit of reversed magnetization itself (represented by an activation magnetic moment).
To further aid the goals of minimization, and prevent the creation of a superparamagnetic state, each magnetic grain must have a relatively large value for energy of magnetic anisotropy. This large energy value materially aids creation of the magnetic characteristic (large Hc/Mrt value) essential for high-resolution recording.
Unfortunately, to achieve the objective of the above-described granular structure (high SNR), where magnetic grains with high energy of magnetic anisotropy are dispersed in a non-magnetic matrix, very rigorous requirements must be met.
In conventionally used Coxe2x80x94Cr alloy magnetic films, chromium is segregated from a cobalt alloy magnetic grain toward a grain boundary by deposition at high temperature. This process reduces magnetic interaction between the magnetic grains. Additionally, since the grain boundary phase in the granular magnetic layer is a non-magnetic non-metallic substance, the segregation more easily occurs than with conventional chromium. Consequently, magnetic grain isolation is easily enhanced.
In a conventional Coxe2x80x94Cr alloy magnetic layer, heating the substrate over about 200xc2x0 C. is essential for sufficient segregation of chromium when laminating the magnetic layer. In the above-mentioned method of Japanese Patent No. 2806443, heating the substrate to a temperature between 60 to 150xc2x0 C. was necessary. The disclosed granular magnetic layer had the advantage of allowing partial segregation of the non-magnetic non-metallic substance in lamination without heating.
Unfortunately, formation of magnetic recording mediums having a granular magnetic layer requires adding a relatively large amount of platinum to the cobalt alloy. This large amount of platinum allows the magnetic recording medium to obtain the desired magnetic characteristics, particularly high coercive force Hc. Specifically, to attain a desired coercive force Hc of 2,800 Oe, additions of as high as 16 at % platinum is needed. This additional platinum is very expensive. In the conventional CoCr metallic magnetic films, only about 8 at % platinum is added to obtain the same value of Hc.
With rising recording density demand, high He over 3,000 Oe are desirable. This demand unfortunately leads to use of additional platinum and increased manufacturing costs, both contrary to a desire for lower price.
As a further manufacturing difficulty, adding platinum increases media noise, also contrary to consumer demand. Consequently, additional control of the granular magnetic layer is necessary to reduce media noise and costs.
It is an object of the present invention to provide a magnetic recording medium and manufacturing method which overcomes the drawbacks of the related art noted above.
It is another object of the present invention to provide a method for manufacturing a magnetic recording medium, having a granular magnetic layer, and exhibiting high coerce force, low cost, and low media noise.
It is another object of the present invention to provide a magnetic recording medium manufactured by the present method.
The present invention relates to a magnetic recording medium and method for manufacturing which achieves excellent magnetic recording characteristics by sequentially sputtering a non-magnetic under-layer, a non-magnetic intermediate layer, and a magnetic layer on a substrate in an atmosphere of H2O partial pressure of 2xc3x9710xe2x88x9210 Torr or lower. This process allows beneficial deposition of the magnetic layer and reduces raw materials costs. The magnetic layer includes ferromagnetic grains and non-magnetic grain boundaries. The intermediate layer has a hexagonal close-packed crystal structure. The manufacturing method allows manufacture of a high quality magnetic recording medium without a heating step thereby allowing lower cost materials use, reducing time, and increased savings.
According to one embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, comprising the steps of: laminating a non-magnetic under-layer on the non-magnetic substrate by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, laminating a non-magnetic intermediate layer on the non-magnetic under-layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, laminating a magnetic layer on the intermediate layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the magnetic layer comprising at least ferromagnetic grains and grain boundaries surrounding the grains, laminating a protective layer on the magnetic layer, and laminating a liquid lubricant layer on the protective layer.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the non-magnetic intermediate layer is made of at least a metal selected from the group consisting of Ti, Cr, Zr, Hf, Ti alloy, Cr alloy, Zr alloy and Hf alloy, and the non-magnetic intermediate layer has a hexagonal close-packed crystal structure.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the non-magnetic intermediate layer has a thickness of from 0.5 nm to 20 nm.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the non-magnetic grain boundary is composed of at least one of an oxide and a nitride of at least one element selected from the group consisting of Mg, Al, Si, Ti, Cr, Mn, Co, Zr, Ta, W and Hf.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the under-layer is composed of at least one of chromium and a chromium alloy.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the non-magnetic substrate is composed of a material selected from the group consisting of a crystallized glass, a chemically strengthened glass and a plastic.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, wherein: the steps of laminating the non-magnetic under-layer, laminating the non-magnetic intermediate layer, laminating the magnetic layer, the step of laminating the protective layer, and the step of laminating the liquid lubricant layer are conducted without a step of heating.
According to another embodiment of the present invention there is further provided a magnetic recording medium, manufactured by a method for manufacturing a magnetic recording medium.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, comprising the steps of: selecting a non-magnetic substrate, laminating a non-magnetic under-layer on a non-magnetic substrate by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, laminating a non-magnetic intermediate layer on the non-magnetic under-layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the non-magnetic intermediate layer made of at least a metal selected from the group consisting of Ti, Cr, Zr, Hf, Ti alloy, Cr alloy, Zr alloy and Hf alloy, the non-magnetic intermediate layer having a hexagonal close-packed crystal structure, and the non-magnetic intermediate layer having a thickness of from 0.5 nm to 20 nm, laminating a magnetic layer on the intermediate layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the magnetic layer comprising at least ferromagnetic grains and grain boundaries surrounding the grains, laminating a protective layer on the magnetic layer, and laminating a liquid lubricant layer on the protective layer.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, comprising the steps of: selecting a non-magnetic substrate, laminating anon-magnetic under-layer on a non-magnetic substrate by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, laminating a non-magnetic intermediate layer on the non-magnetic under-layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the non-magnetic intermediate layer made of at least a metal selected from the group consisting of Ti, Cr, Zr, Hf, Ti alloy, Cr alloy, Zr alloy and Hf alloy, the non-magnetic intermediate layer having a hexagonal close-packed crystal structure, and the non-magnetic intermediate layer having a thickness of from 0.5 nm to 20 nm, laminating a magnetic layer on the intermediate layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the magnetic layer comprising at least ferromagnetic grains and grain boundaries surrounding the grains, laminating a protective layer on the magnetic layer, laminating a liquid lubricant layer on the protective layer, and conducting the steps of laminating without a step of heating.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, comprising the steps of: selecting a non-magnetic substrate, laminating a non-magnetic under-layer on a non-magnetic substrate by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, laminating a non-magnetic intermediate layer on the non-magnetic under-layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the non-magnetic intermediate layer made of at least a metal selected from the group consisting of Ti, Cr, Zr, Hf, Ti alloy, Cr alloy, Zr alloy and Hf alloy, the non-magnetic intermediate layer having a hexagonal close-packed crystal structure, and the non-magnetic intermediate layer having a thickness of from 0.5 nm to 20 nm, laminating a magnetic layer on the intermediate layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the magnetic layer comprising at least ferromagnetic grains and non-magnetic grain boundaries surrounding the grains, the non-magnetic grain boundaries being composed of at least one of an oxide and a nitride of at least one element selected from the group consisting of Mg, Al, Si, Ti, Cr, Mn, Co, Zr, Ta, W and Hf, laminating a protective layer on the magnetic layer, and laminating a liquid lubricant layer on the protective layer.
According to another embodiment of the present invention there is provided a method for manufacturing a magnetic recording medium, comprising the steps of: selecting a non-magnetic substrate, laminating a non-magnetic under-layer on a non-magnetic substrate by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, laminating a non-magnetic intermediate layer on the non-magnetic under-layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the non-magnetic intermediate layer made of at least a metal selected from the group consisting of Ti, Cr, Zr, Hf, Ti alloy, Cr alloy, Zr alloy and Hf alloy, the non-magnetic intermediate layer having a hexagonal close-packed crystal structure, and the non-magnetic intermediate layer having a thickness of from 0.5 nm to 20 nm, laminating a magnetic layer on the intermediate layer by sputtering in an atmosphere having a partial pressure of H2O of 2xc3x9710xe2x88x9210 Torr or below, the magnetic layer comprising at least ferromagnetic grains and non-magnetic grain boundaries surrounding the grains, the non-magnetic grain boundaries being composed of at least one of an oxide and a nitride of at least one element selected from the group consisting of Mg, Al, Si, Ti, Cr, Mn, Co, Zr, Ta, W and Hf, laminating a protective layer on the magnetic layer, laminating a liquid lubricant layer on the protective layer, and conducting the steps of laminating without a step of heating.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.